In a letter to President Obama's assistant for science and technology, four UCSF professors who are experts in biophysics, imaging, and cancer have expressed concern over the potential for severe health effects due to whole body back scatter X-ray airport security scanners. They call for an urgent review of the safety of these devices, which they argue have not been adequately evaluated for human safety.
Despite the widespread use of these whole body X-ray scanners and the lack of proven safety of these devices, the Food and Drug Administration (FDA) has failed to take these machines off the market until they are proven to be safe and effective. In contrast, the FDA has threatened to enforce a ban on electronic cigarettes, which have been shown to be much safer than cigarettes and which appear to be relatively safe and effective for smoking reduction or cessation.
Today, I am questioning the consistency of the FDA's regulation of medical devices and the role of politics, rather than purely scientific and public health considerations, in shaping the Agency's policy and actions.
The UCSF scientists who co-authored the letter include a Professor Emeritus of Biochemistry and Biophysics at UCSF, with expertise in imaging; an internationally renowned cancer expert; and two professors who are X-ray crystallographers and imaging experts.
The UCSF scientists write: "We are writing to call your attention to serious concerns about the potential health risks of the recently adopted whole body backscatter X-ray airport security scanners. This is an urgent situation as these X-ray scanners are rapidly being implemented as a primary screening step for all air travel passengers. Our overriding concern is the extent to which the safety of this scanning device has been adequately demonstrated. This can only be determined by a meeting of an impartial panel of experts that would include medical physicists and radiation biologists at which all of the available relevant data is reviewed."
"An important consideration is that a large fraction of the population will be subject to the new X-ray scanners and be at potential risk, as discussed below. This raises a number of ‘red flags’. Can we have an urgent second independent evaluation?"
"The physics of these X-rays is very telling: the X-rays are Compton-Scattering off outer molecule bonding electrons and thus inelastic (likely breaking bonds). Unlike other scanners, these new devices operate at relatively low beam energies (28keV). The majority of their energy is delivered to the skin and the underlying tissue. Thus, while the dose would be safe if it were distributed throughout the volume of the entire body, the dose to the skin may be dangerously high. The X-ray dose from these devices has often been compared in the media to the cosmic ray exposure inherent to airplane travel or that of a chest X-ray. However, this comparison is very misleading: both the air travel cosmic ray exposure and chest Xrays have much higher X-ray energies and the health consequences are appropriately understood in terms of the whole body volume dose. In contrast, these new airport scanners are largely depositing their energy into the skin and immediately adjacent tissue, and since this is such a small fraction of body weight/vol, possibly by one to two orders of magnitude, the real dose to the skin is now high."
"In addition, it appears that real independent safety data do not exist. A search, ultimately finding top FDA radiation physics staff, suggests that the relevant radiation quantity, the Flux [photons per unit area and time (because this is a scanning device)] has not been characterized. Instead an indirect test (Air Kerma) was made that emphasized the whole body exposure value, and thus it appears that the danger is low when compared to cosmic rays during airplane travel and a chest X-ray dose. In summary, if the key data (flux-integrated photons per unit values) were available, it would be straightforward to accurately model the dose being deposited in the skin and adjacent tissues using available computer codes, which would resolve the potential concerns over radiation damage."
In addition, the scientists point out that "The large population of older travelers, >65 years of age, is particularly at risk from the mutagenic effects of the X-rays based on the known biology of melanocyte aging."
Furthermore, "A fraction of the female population is especially sensitive to mutagenesis provoking radiation leading to breast cancer. Notably, because these women, who have defects in DNA repair mechanisms, are particularly prone to cancer, X-ray mammograms are not performed on them. The dose to breast tissue beneath the skin represents a similar risk.
Moreover, "The population of immunocompromised individuals--HIV and cancer patients (see above) is likely to be at risk for cancer induction by the high skin dose."
The letter also expresses concern over lack of data on the safety of these devices for pregnant women, the risk of testicular cancer induction, and the effects on the cornea and thymus.
Finally, "The risk of radiation emission to children and adolescents does not appear to have been fully evaluated."
The letter explains that: "Because this device can scan a human in a few seconds, the X-ray beam is very intense. Any glitch in power at any point in the hardware (or more importantly in software) that stops the device could cause an intense radiation dose to a single spot on the skin. Who will oversee problems with overall dose after repair or software problems?"
The letter concludes that: "there has not been sufficient review of the intermediate and long-term effects of radiation exposure associated with airport scanners. There is good reason to believe that these scanners will increase the risk of cancer to children and other vulnerable populations. We are unanimous in believing that the potential health consequences need to be rigorously studied before these scanners are adopted."
Concerned about the potential effects of the cumulative radiation dose for frequent fliers, the U.S. Airline Pilots Association has asked the TSA to exempt pilots from the scans. Many radiation health experts are also refusing to undergo the whole body X-ray screening because of the lack of sufficient demonstration of the safety of these devices.
According to a letter from Ralph Nader to the Department of Homeland Security, demanding Congressional hearings on the safety of airport X-ray scanners: "Dr. David Brenner, director of Columbia University's Center for Radiological Research, has cautioned [against] using a technology that would expose millions of air travelers to radiation. Dr. Brenner was a member of the 2002 government panel that set radiation safety guidelines for the airport scanners. He now says he would not have signed the report if he had known that TSA planned to X-ray virtually every airline passenger."
Moreover, there are serious privacy and civil liberty concerns as well as effectiveness concerns regarding the use of these devices.
Senator Susan Collins (R-Maine) also sent a letter to the Department of Homeland Security and the TSA expressing serious concerns about the safety of airport X-ray scanners and demanding a scientific safety review. The letter noted: "Given that these concerns have been brought to the Department’s attention on several occasions, it is troubling that TSA announced in May it would purchase an additional 100 backscatter x-ray AIT machines. Please explain why the Department continues to purchase this technology when legitimate concerns about its safety appear to remain unanswered."
The Rest of the Story
I believe that there is very strong reason to believe that the safety of whole body back scatter X-ray scanners has not been adequately demonstrated. Moreover, there is credible concern over the potential that these devices may increase cancer risk among vulnerable populations. It is quite clear, therefore, that the FDA should not have approved of the marketing and use of these devices. These products should be removed from the market until their safety has been demonstrated.
Instead of demanding adequate safety demonstration data from the manufacturers of these whole body back scatter X-ray scanners, which are being used on literally millions of people on almost a daily basis, the FDA has apparently been pre-occupied with trying to remove electronic cigarettes from the market until their safety has been proven, even though there is no reason to suspect that they are harming users.
Where is the American Cancer Society in calling for the removal of whole body X-ray scanners from the market? The ACS has vigorously denounced the sale of electronic cigarettes and called for these products to be removed from the market, even though not a single carcinogen has been shown to be present in these products at more than trace levels. In contrast, there is a legitimate concern over the potential for whole body X-ray scanners to increase cancer risk in the population, yet the ACS has apparently not called for the removal of these devices from the market.
Why the terrible inconsistency in the way the FDA, and the national health groups, are treating different products?
The answer, I believe, is politics.
For the FDA, there is a simple solution. According to a Boston Globe article: "There is another type of full body scanner called a millimeter wave scanner, which doesn't use X-rays, and poses less of a safety concern, according to biophysicist David Brenner, director of the Center for Radiological Research at Columbia University Medical Center in New York City." Since this device poses no cancer risk, it appears that the X-ray scanner is an unsafe device and should not be approved for use.
If it were only science, and not politics, that were dictating policy, the FDA would have removed the X-ray scanners from public use long ago, and would have demanded that adequate data be presented to demonstrate the safety of these devices among vulnerable population groups. The FDA would have demanded to see the type of data that the UCSF researchers have called for.
If it were only science, and not politics, that were dictating policy, the American Cancer Society would have called for the removal of these X-ray scanners from the market - along with electronic cigarettes (or it would not have called for a ban on either product).
For the ACS - at least - money is also an apparent factor. The ACS receives money from Big Pharma companies that manufacture smoking cessation drugs and stand to lose substantial sales if electronic cigarettes become popular.
The approval of whole body X-ray scanners for use on nearly a million people a day in the United States, coupled with the ban on electronic cigarettes - which save tens of thousands of people a day from exposure to the carcinogens in tobacco smoke - represents one of the largest inconsistencies in federal public health policy of which I am aware.
It is only January 3, but the FDA and the American Cancer Society are well on their way to putting themselves into contention for the Tobacco Control Hypocrisy Award of 2011.
Also in line for the hypocrisy award is the office of the United States Surgeon General, which has warned that there is no safe level of exposure to secondhand smoke because even minute exposure to a potential carcinogen is dangerous. Why, then, has the Surgeon General not called for the immediate removal of X-ray scanners from airports? After all, by her logic, there is no safe level of exposure to X-rays. Nearly a million U.S. residents per day are put at risk by being exposed to potentially carcinogenic whole body radiation in airports. Yet so far as I am aware, the Surgeon General has expressed no concerns or even discomfort with these mandatory procedures that expose millions of Americans to potential cancer-inducing X-rays almost daily.